Generally, a motor grader is a wheeled construction machine which levels land such that a road surface, a ground surface and the like become smooth ground surface. A blade for leveling a ground surface can move in the vertical direction, incline in the vertical direction, incline in the front-rear direction of the vehicle, slide in the right-and -left direction of the vehicle, and turn around a predetermined pivot shaft.
Generally, the motor grader has a structure as shown in a perspective view in FIG. 10. FIG. 10 shows a conventional example of the present invention. As shown in FIG. 10, one end of a draw bar 103 is connected to a front end of a front frame 102 of a motor grader 101 such that the draw bar 103 can swing around the one end thereof.
A swing circle 109 is mounted on the draw bar 103 such that the swing circle 109 can swing, and a blade 105 is supported by the swing circle 109 such that the blade 105 can slide in the lateral direction. One ends of a pair of left and right lift cylinders 111a and 111b are turnably connected to the draw bar 103. Portions of the lift cylinders 111a and 111b which are turnably connected to lifter brackets 107 are close to the draw bar 103. The lifter brackets 107 are mounted on the front frame 102.
A draw bar shift cylinder 112 is disposed between the lifter bracket 107 and the draw bar 103. The blade 105 is supported by the swing circle 109 through a guide (not shown). A side shift cylinder (not shown) is disposed between the blade 105 and the guide. The blade 105 can slide in the lateral direction of the vehicle by expansion and contraction of the side shift cylinder.
By expanding and contracting the pair of left and right lift cylinders 111a and 111b in synchronization with each other, the draw bar 103 can be moved upward and downward. That is, the blade 105 can be moved vertically. If the pair of left and right lift cylinders 111a and 111b is expanded and contracted differently from each other, the draw bar 103 can be inclined in the vertical direction. That is, the draw bar 103 can be inclined in a state where one end of the blade 105 is raised and the other end thereof is lowered.
By expanding and contracting the draw bar shift cylinder 112, the draw bar 103 can be swung in the right-and-left direction of the vehicle. The swing circle 109 is swung by a hydraulic motor 116. By swinging the swing circle 109, the blade 105 supported by the swing circle 109 can swing in the clockwise direction or the counterclockwise direction as viewing the draw bar 103 from above of the vehicle. The swinging angle of the swing circle 109 may exceed 360° and the swing circle 109 may continuously swing if necessary.
A tilt angle of the blade 105 with respect to the ground surface can be varied by expanding and contracting a tilt cylinder (not shown). Since the motor grader has such a structure, the blade 105 can control the up-and-down movement, up-and-down inclination, right-and-left swing, rotation, right-and-left sliding movement and tilting movement of the blade 105 with respect to the vehicle through the draw bar 103 and the swing circle 109.
Patent Document 1: Japanese Patent Laid-open Publication No. 2004-190232